Photochromic and thermochromic ink formulations are known in the patent literature, primarily for screen printing applications but also for security inks. By way of example, U.S. Pat. No. 5,591,255 issued to Small et al. describes thermochromic ink formulations and their methods of use. U.S. Pat. No. 5,017,225, issued to Nakanishi et al. describes microencapsulated photochromic material, together with a process for its preparation in a water-base ink composition. U.S. Pat. No. 4,927,180, issued to Trundle et al describes marking of articles with photochromic compounds. U.S. Pat. No. 5,630,869 issued to Amon et al describes reversibly photochromic printing inks. U.S. Pat. No. 7,351,362 issued to Yasuda et al. describes various photochromic materials. Photochromic ink formulations for metal decorating applications are conspicuously missing from the patent literature.
Fluorescent ink formulations are also known in the patent literature. These most often pertain to ink jet inks, but fluorescent inks are also used for security applications. Fluorescent metal decorating offset inks are conspicuously missing from the patent literature. By way of example, U.S. Pat. No. 4,150,997, issued to Hayes describes a water base fluorescent ink for ink jet printing, U.S. Pat. No. 5,256,192, issued to Liu et al. describes a solvent based fluorescent ink composition for ink jet printing. U.S. Pat. No. 7,141,105 issued to Udagawa et al. describes a water-based fluorescent ink, a recorded image using the ink, and a judging method. U.S. Pat. No. 5,445,671, issued to Herget et al. describes an offset printing ink.
Near infrared absorbing dyes have been incorporated into inks and used to enhance document security. Many of these formulations rely on detecting the near infrared fluorescence emission of dyes rather than monitoring NIR absorbance intensity. For example, U.S. Pat. No. 5,684,069, issued to Auslander describes a composition for invisible ink that is responsive to infrared light. U.S. Pat. No. 5,460,646, issued to Lazzouni et al. describes an infrared printing ink. U.S. Pat. No. 6,706,460 B1 describes stable IR dye compositions for invisible marking.